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Without stoppage, a train travels a certain distance with an average speed of 60 km/h, and with stoppage, it covers the same distance with an average speed of 40 km/h. On an average, how many minutes per hour does the train stop during the journey?

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    $\begingroup$ Hint. Just imagine that the "certain distance" is 60km, so the trip takes one hour. $\endgroup$ – Ethan Bolker Dec 3 '16 at 13:24
  • $\begingroup$ You are assuming that the train travels at either $60$ km/h or $0$ km/h with no acceleration or deceleration $\endgroup$ – Henry Dec 3 '16 at 13:32
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As distance is same.

D = S * T

Let t = usual time s = stop time

60t = 40 (t+s).

60t - 40t = 40s

20t = 40s

t = 2s

Here total time is 1 hour or 60 minutes.

So, t + s = 60 minutes

2s + s = 60

3s = 60

s = 20

So train stops for 20 minutes.

One trick that I use to solve this type of question.

Difference in two speeds is 20 kmph. Which is 1/3rd of original speed. So find the 1/3rd of 1 hour or 60 minutes. Which is 20 minutes.

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